1. Field of the Invention
The present invention relates to a toner for use in developing electrostatic latent images prepared by a method such as electrophotography, electrostatic recording and electrostatic printing. More particularly, the present invention relates to a toner for use in image forming apparatus such as copiers, printers and plain paper facsimiles, which utilize a direct or indirect developing method. In addition, the present invention also relates to a method for manufacturing the toner, an image forming apparatus and a process cartridge using the toner, and a method and a device for packing the toner.
2. Discussion of the Background
In electrophotographic image forming apparatus, images are typically formed by the following method:    (1) an image bearing member such as photoreceptors is charged with a charger (charging process);    (2) the charged image bearing member is exposed to imagewise light to form an electrostatic latent image on the image bearing member (light irradiating process);    (3) the electrostatic latent image is developed with a developer including a toner to form a toner image on the image bearing member (developing process);    (4) the toner image is transferred onto a receiving material optionally via an intermediate transfer medium (transfer process);    (5) the toner image is fixed on the receiving material by a fixing device upon application of heat, pressure and/or the like (fixing process); and    (6) toner particles remaining on the image bearing member even after the transfer process are removed by a cleaner so that the image bearing member can be ready for the next image forming processes.
Recently, images formed by electrophotography are requested to have high image qualities (especially, good image reproducibility) whether the images are monochrome images or color images. In particular, half tone images typically have a large image area proportion in full color images. Therefore, by improving image reproducibility of color toners, various color images can be faithfully reproduced. In attempting to produce high quality color images having good evenness and good color reproducibility, toners having a small particle diameter and/or a spherical form have been proposed and developed.
Published unexamined Japanese Patent Applications Nos. (hereinafter JP-As) 2002-148863, 05-313416 and 02-148046 have disclosed methods for manufacturing a spherical toner which include the following processes:    (1) mother toner particles including at least a binder resin and a colorant are dispersed in water or an aqueous solvent including a dispersant to prepare a dispersion;    (2) a mixture of a softening agent which can soften the mother toner particles, and an organic solvent which can be mixed with water or the aqueous solvent and can dissolve the softening agent is added to the dispersion so that the mother toner particles absorb the softening agent; and    (3) the softening agent is removed from the mother toner particles.
By using these methods, spherical toners having a proper particle diameter distribution can be prepared without particularly limiting the binder resin.
However, the toners prepared by these methods have a drawback in that toner particles tend to invade into a gap between an image bearing member (e.g., a photoreceptor) and a cleaner (e.g., a cleaning blade) because of easily rolling (i.e., because of having an excessive rolling property), thereby causing a cleaning problem in that undesirable streak images are produced in the resultant images. In addition, the toners have a drawback in that when a dot image is developed and transferred, toner particles in a dot image scatters around the dot image due to their excessive rolling property, resulting in formation of toner scattering images.
In addition, JP-As 61-22354, 06-250439 and 09-68823 have disclosed toners which include toner particles including a colorant and a binder resin, wherein the toner particles have a volume average particle diameter of from 3 to 9 μm and a specific particle diameter distribution.
By using the toners having such a small particle diameter, images having good evenness can be produced without causing a background development problem in that the resultant images have background fouling which is caused by undesirable charge properties of the toners.
However, the toners have a drawback in that toner particles tend to invade into a gap between a photoreceptor and a cleaner in the cleaning process, resulting in occurrence of the cleaning problem. If the toners have an irregular form, the toners do not cause the cleaning problem. However, another problem occurs in that the resultant images have poor fine line reproducibility because toner particles move differently in the image developing process and the image transfer process.
In addition, JP-A 2002-207317 discloses a toner having a flat form. The toner is prepared by the following method:    (1) resin particles having an average primary particle diameter of from 10 to 500 nm is subjected to a salting-out/fusion treatment to prepare secondary particles of the resin; and    (2) the secondary resin particles are flattened to prepare the flat toner.
By using this flat toner, high image-density and high quality images having smooth surface can be produced without forming the toner-scattering problem mentioned above.
However, the toner has poor fluidity, and thereby the toner particles cannot be densely and uniformly arranged in a dot toner image. Therefore, when images are formed at a high dot (or linear) density, the toner images have poor dot reproducibility. The same is true for toners having an irregular form.
JP-A 07-152202 discloses a polymer solution dispersing method using a polymer solution dispersing technique utilizing shrinkage of the dispersed polymer solution. Specifically, the method is as follows:    (1) a toner constituent mixture including toner constituents such as binder resins and colorants is dispersed or dissolved in a volatile solvent such as organic solvents having a low boiling point to prepare a toner constituent mixture liquid;    (2) emulsifying the toner constituent mixture liquid in an aqueous medium including a dispersant to prepare drops of the toner constituent mixture liquid in the aqueous medium; and    (3) removing the volatile solvent, resulting in shrinkage of the liquid drops and formation of toner particles.
When a solid particulate material which is not dissolved in the aqueous medium is used as the dispersant, the resultant toner particles have an irregular form. However, when the solid content of the toner constituent mixture liquid is increased to improve the productivity, the viscosity of the toner constituent mixture liquid seriously increases, and thereby the average particle diameter of the resultant toner particles increases and the particle diameter distribution thereof is also broadened. If a resin having a low molecular weight is used as the binder resin to decrease the viscosity, a problem in that the fixability (particularly, the hot offset resistance) of the resultant toner deteriorates occurs.
JP-A 11-149179 discloses a modified polymer solution dispersing method in which a resin having low molecular weight is included in the toner constituent mixture liquid to decrease the viscosity of the toner constituent mixture liquid (resulting in easy emulsification of the toner constituent mixture liquid) and the low molecular weight resin is subjected to a polymerization reaction in the liquid drops to improve the fixability of the resultant toner. However, the method has drawbacks in that the resultant toner particles have broad particle diameter distribution; the surface of the toner particle is not smooth; and the shape of the toner particles cannot be controlled.
Because of these reasons, a need exists for a toner which has good cleanability and which can produce high quality images without causing the fogging problem and without deteriorating fine dot reproducibility.